Far north, where water falls not as rain but as snow, is a pass through the mountains, these mountains are the boarder of the mighty Empire and the lawless Barbarians
It must be kept and ever patrolled unless they want the entire empire ravished and laid waste, so for every 6 hours a new squad of hardened troops march up the poorly-kept road and interrogate travellers and hold of plans to topple the great structure gatehouse, built to prevent these hairy barbarians from getting their dreams.
And that is how it must stay...

And the portcullis actually goes up and down, But I apologise for the terrible quality video and poor focus: